dm: pinctrl: migrate pinctrl-generic to livetree

dm: pinctrl: migrate pinctrl-generic to livetree

Migrate pinctrl-generic to livetree:
- dev_for_each_property
- dev_read_prop_by_prop
- dev_read_string_count
- dev_read_string_index
and get rid of DECLARE_GLOBAL_DATA_PTR.

This patch solves the parsing issue during sandbox tests for pin
configuration (OF_LIVE is activated in sandbox_defconfig
and sub node are not correctly parsed in
pinctrl_generic_set_state_subnode with fdt lib API).

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>